New Study Explains How Vaccine Scares Unfold

April 05, 2012 - News Release

Worries over vaccine risks can allow preventable contagious diseases, such as measles and whooping cough, to make a comeback. A new study by a University of Guelph professor, published today in PLoS Computational Biology, shows how to predict ways in which population vaccinating behaviour might unfold during a vaccine scare.

“These findings might help in evaluating and developing global immunization programs and public health policy,” said Prof. Chris Bauch of Guelph’s Department of Mathematics and Statistics. PLoS Computational Biology is a peer-reviewed international journal published by the Public Library of Science.

Bauch and Samit Bhattacharyya of the University of Utah developed a mathematical, “behavior-incidence” model based on game theory and social learning.

They tested the model with real data from two infamous vaccine scares in England and Wales: the 1970s pertussis outbreak and the measles-mumps-rubella vaccine scare in the 1990s. In both cases, the publication of alleged vaccine risks was followed by a media firestorm in national newspapers, television, and radio. In light of this, the fact that it took four to five years for vaccine uptake to bottom out was puzzling. The researchers found that the model could explain the patterns of the vaccine scare and be applied predicatively to the data sets.

The model captured the interplay between disease dynamics and vaccination behaviour during those episodes. One of the theoretical dynamics for the model was the phenomenon known as “herd immunity”; an entire population — unvaccinated individuals — can be protected from infection by vaccinating only a certain percentage of the population.

Bauch said that this suggests that immunization programs can be victims of their own success as past vaccinations drive disease incidence to such low levels that unvaccinated individuals feel no incentive to get vaccinated, creating ideal conditions for vaccine scare and thus future outbreaks.

“Our results show that strategic interactions between individuals and social learning may be crucial governing mechanisms of the population’s response to a vaccine scare, in addition to changes in risk perception,” Bauch said.

As a result, vaccine scares could become more common as eradication goals are approached for more vaccine-preventable diseases, he said.

“Models such as ours could help us predict how vaccine scares might unfold, including vaccine coverage and disease incidence, and assist in mitigation efforts.”

Chris Bauch
Department of Mathematics and Statistics
519-823-4120, Ext. 53079

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